Consensus promoter sequences: AATTAACCCTCACTAAA G GGAGA–T3 TAATACGACTCACTATA G GGAGA–T7 ATTTAGGTGACACTATA G AAGNG–SP6 The position in bold (+1) indicates the first nucleotide incorporated into RNA during transcription. Only bases at this position through +3 are critical for transcription, and they must be a G and a purine base, respectively (9).